As it has become evident that the formation of a lipoperoxide in the body and a concomitant radical reaction have various harmful effects on the living body through membrane disorders, enzymatic disorders and the like, various attempts to use antioxidants and lipoperoxide formation inhibitors as medicines have been made. At present, the main lipoperoxide formation inhibitors used in the art are derivatives of natural antioxidants such as vitamin C, vitamin E and the like, and phenol derivative. However, their fundamental structural skeletons are limited and they are not necessarily satisfactory in practical use. Thus, it is requested to develop a lipoperoxide formation inhibitor having a novel structure so that it can be widely utilized in the medicinal field.
Under these circumstances, the present inventors synthesized a number of novel compounds and tested their lipoperoxide formation inhibitory activities, respectively. As a result, the present inventors found that certain thiazolo[5,4-b]azepine derivatives had antioxidation activity and lipoperoxide inhibitory activity, and filed a patent application (EP-A-0 351 856). Then, the present inventors further intensively studied to find out additional novel compound having the above activities. As a result, the present inventors have succeeded in the synthesis of the novel condensed thiazole derivatives of the formula [I] shown hereinafter and salt thereof. Further, it has been found that such novel compounds have activities useful for medicines, for example, strong lipoperoxide formation inhibitory activity, inhibition activity of 12-hydroxyheptadecatrienic acid (hereinafter abbreviated as HHT) and lipoxygenase, leukotriene D.sub.4 (LTD.sub.4) receptor antagonistic activity and the like. Thus, the present invention has been completed.